Damaged tissues are sometimes treated using an energy delivering system. Various types of therapeutic energies (e.g., electrical, ultrasonic, microwave, cryogenic, heat, laser, etc.) used in tissue treatment, which are known in the art, may be applied to treat a tissue. Electrosurgery is a tissue treating technique involving delivering of high radio frequency (“RF”) electrical energy (e.g., 1-70 watts in auto bipolar electrosurgical systems, 1-300 watts in monopolar electrosurgical systems). Electrosurgery treatment is rendered by an electrosurgical device (e.g., electrosurgical forceps).
Electrosurgical systems conventionally monitor an electrical voltage and an electrical current in order to ‘remotely’ evaluate the impedance at the electrosurgical device. Evaluation of the impedance at the electrosurgical device enables an electrosurgical system to detect whether the electrosurgical system is in an ‘open circuit’ state in which the electrosurgical device does not touch the treated site, or in a ‘closed circuit’ state in which the electrosurgical device touches the treated site. Distinguishing between these two states enables the electrosurgical system to output (generate) therapeutic energy only when the electrosurgical device touches the treated site.
When the surgical device touches a tissue, the impedance evaluated by the electrosurgical system is relatively low (a few tenths of ohms to several thousands of ohms). When the surgical device is detached from a treated tissue, the impedance measured by the electrosurgical system should ideally be infinite (or practically very high; e.g., in the order of tenths of mega ohms). Should this be the case, an impedance gap between the open circuit state and the closed circuit state would have been very large, which would enable the electrosurgical system to distinguish between the two states easily and reliably. However, in practice, the electrosurgical system's periphery, which may include, for example, cable(s), adapter(s), connector(s), surgical device(s), etc., includes parasitic (leakage) impedances that detrimentally affect the impedance gap, that is, they narrow the gap. Depending on the electrical characteristics of the electrosurgical system's periphery, the impedance undesirably imposed by it may vary, for example, from tenths of ohms to tenths of kilo ohms.
The parasitic (e.g., leakage) impedance imposed on the electrosurgical system by its periphery poses a problem which is that the electrosurgical system, which monitors the impedance during electrosurgical procedures, might erroneously interpret a parasitic impedance as an impedance that results from a tissue contact even in cases where the electrosurgical device does not touch the tissue. As a result of this, the electrosurgical system might erroneously continue to deliver therapeutic energy to the electrosurgical device, or resume delivery of the therapeutic energy, even though the device (e.g., forceps) is not touching the surgical site. Holding the treatment device by a surgeon may also add parasitic impedance, which exacerbates the problem of misinterpretation of the impedance evaluated by the electrosurgical system. (The surgeon may hold the device prior to treatment and then during treatment, and, occasionally, s/he may detach it from the treated tissue and, therefore, a parasitic impedance caused by the surgeon might change during the electrosurgical process as well.)
Because, conventionally, the electrical voltage and current that the electrosurgical system uses to evaluate the impedance at the electrosurgical device, hence the device-tissue contact degree, do not genuinely represent the real impedance at the electrosurgical device (due to the aforesaid parasitic/leakage capacitances), not only that distinguishing between the open circuit state and the closed circuit state might not be reliable, the electrosurgical system might deliver/output therapeutic/treatment energy to the tissue which is not therapeutically optimal.
It would be beneficial to have a method and system that enable reliable operation of an electrosurgical system despite unknown impedance changes in the electrosurgical system during electrosurgical procedures.